The present invention constitutes an improvement over the inventions of both U.S. Pat. No. 3,532,422 issued Oct. 6, 1970 entitled "Method and Apparatus for Electrostatic Color Reproduction" by Samuel B. McFarlane, assignor to ElectroPrint, Inc., the assignees of the instant invention; and the co-pending commonly assigned application of Pressman and Kittredge U.S. Ser. No. 800,236 filed on Feb. 18, 1969 entitled "Method and Apparatus for Aperture Controlled Electrostatic Image Color Reproduction or Constitution." The prior art includes Kaprelian U.S. Pat. No. 2,986,466; Lusher U.S. Pat. No. 3,399,611; Frank U.S. Pat. No. 3,680,954; and Snelling U.S. Pat. No. 3,288,602.
McFarlane U.S. Pat. No. 3,532,422 relating to "Methods and Apparatus for Electrostatic Color Reproduction" employs latent electrostatic charged images formed on a photoconductive interrupted surface such as a grid or screen. The imaged screen is dusted with charged colored toner marking materials, thus developing the image but leaving it in an unfixed state on the screen, and then the developed toner image or pattern is projected by electrical field across an air gap onto a print receiving medium. In the preferred arrangement, multicolor printing is accomplished by uniformly charging the photoconductive surface and then optionally projecting a first primary color image thereupon. This image is then developed by powdering it in a first color and the powder pattern transferred substantially intact by electrical field across the air gap onto the paper or other material to be printed. Then the second and third primary color images are laid down in the same manner so that the resulting reproduction exhibits all the colors of the multicolor original. Fixing may occur between colors or at the end.
The assignee's pending U.S. application Ser. No. 800,236 is also concerned with multicolor electrostatic reproducing or constituting. Here again, an interrupted photoconductive surface, such as a screen, is employed to carry charge distribution in accordance with selected color separation patterns. In a preferred embodiment, tone particles directed at the screen pass therethrough under modulation control dictated by the charge pattern. The patterns are determined by separating the colors of the original into primary color components and those patterns are developed on the print receiving medium in sequence and registry with appropriately colored toners. The screen is multilayered and preferably comprises at least an insulative and conductive layer provided with an array of electrostatically sensitive apertures. An electrical propulsion field directs the charged toner particles through the screen to the print receiving medium which is preferably spaced at a distance from the screen. Charge distribution on the screen controls the flow of particles through the apertures, some of the apertures being in effect blocked, partially blocked, unblocked, or enhanced, depending on the local charge level. This occurs for each color separation and the toner patterns which result are applied in sequence on the print receiving medium to reconstitute the image in color.